Development of high-precision Fresnel lenses for alcohol sensing using vat photopolymerization additive manufacturing

Contemporary optical sensors exhibit remarkable sensitivity, swiftly detecting fluctuations in the surroundings, including variations in temperature, pressure, humidity, and volatile organic compounds (VOCs). Herein, a novel Fresnel lens sensor responsive to alcohol has been developed using liquid crystal display-based vat photopolymerization (VPP). The polymer-based lens sensor is developed from transparent resin called hydroxyethyl methacrylate and is designed to collect and focus light through a transmission mode sensing mechanism. Upon exposure to alcohol solutions, the polymeric material undergoes swelling, inducing alterations in both the lens's focal length and the intensity of its focal point. This reversible swelling phenomenon in the polymer is driven by the diffusion of alcohol molecules into the porous medium of the Fresnel lens, consequently modifying the lens's optical response, as quantified by the intensity of transmitted power. The sensitivity of the lens sensor was examined in relation to ethanol, isopropanol, and methanol, resulting in sensitivities of 0.36, 0.33, and 0.23 µW/vol.%, respectively. The response time and low limit of detection (LOD) were observed to be 25–30 min and 5 vol.%, respectively. The manufactured sensor holds promising applications across diverse domains such as healthcare, biomedicine, food and beverages, and enhancing human safety.